When \(x\) , \(p_1\)  and \(p_2\)  are given, the SNR \(\gamma (H)\)  is a very complicated function of \(H\) . It is difficult to strictly prove the monotonically and convexity of this function. As in [1]} and [2]}, we graphically illustrate these properties in Fig. REF , where we show the SINR \(\gamma (H)\)  versus \(H\)  with \(x=100\)  m. Four different scenarios are illustrated, and the corresponding parameters for each scenario are given in [1]}. It can be found from this figure that for each scenario, the SINR value first increases with height \(H\)  and then decreases with \(H\) . As a result, there exists only one maximum point for each scenario, denoted as \(H^\star \) . The value of \(H^\star \)  is the solution to the following equation:
\(\frac{{d\gamma (H)}}{{dH}} = 0.\) 
